Halogen Based Surface Chemistries for Graphene Synthesis
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1259-S17-02
Halogen Based Surface Chemistries for Graphene Synthesis Srikanth Raghavan,1 Timothy C. Nelson,2 Tobias Denig,2 and C. D. Stinespring2 1
Department of Physics, West Virginia University, Morgantown, WV 26506, USA
2
Department of Chemical Engineering, West Virginia University, Morgantown, WV 26506, USA
ABSTRACT Halogen based (CF4 and Cl2) inductively coupled reactive ion etching (ICP-RIE) has been used to selectively etch silicon from 6H-SiC to produce a controlled number of carbon layers. After annealing at temperatures in the range of 550 oC to 1100 oC to reconstruct the near surface layers, x-ray photoelectron spectroscopy has been used to characterize the composition of the films. For the Cl2 based ICP-RIE, two carbon species are observed. One is due to carbon bound as SiC in the substrate and a second which can be attributed to graphene. In the case of CF4 based etching the situation is similar except the second peak is most closely aligned with p-type graphene. This is most likely due to electron transfer from the graphene to the trace levels of fluorine remaining on the surface after annealing. INTRODUCTION Graphene films a few monolayers thick have emerged as a material with the potential to revolutionize the field of carbon electronics. Devices base on these graphene have been studied for use in applications that include high frequency communications [1], high-speed computer technology [2], photonics [3], and gas sensors [4]. The immense potential of graphene based sensors (as well as other types of graphene electronics) has been demonstrated with material either exfoliated from highly ordered pyrolytic graphite (HOPG) [5] or produced by sublimation of Si from α-SiC (i.e., 4H-SiC and 6H-SiC) [6] at temperatures ~1200 oC. Another approach which has been explored involves the use of Ni to catalyze the decomposition of 6H-SiC at lower temperatures [7,8]. The overall goal of our research is the development of a low-temperature synthesis route for large area epitaxial graphene on insulator films based on halogen etching chemistries for semi insulating (SI) 4H-SiC. The results presented in this paper demonstrate the selective etching of Si from the near surface layers of the SiC to produce graphene or the graphene precursor and the ability to control the number of layers in the resulting graphene film. The benefits of this approach to graphene synthesis, in contrast to current practice, are that it can be scaled to substrate wafer size, it eliminates the need to transfer the graphene, it reduces the need for precise control of temperature, and it can be readily integrated with existing semiconductor technology. EXPERIMENTAL APPROACH For the feasibility studies reported in this paper, 6H-SiC rather than SI 4H-SiC has been used to reduce costs. It is expected that the overall etching chemistries of 6H-SiC and SI 4H-SiC will be largely the same. The samples were either 0.5 cm x 0.5 cm or 1 cm x 1cm squares cut from 6H-SiC wafers grown by CREE Research. Prior to etching, the samples were degreased usin
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